Disclosed herein are branched polyarylene ether polymers and processes for preparing these polymers.
In microelectronics applications, there is a great need for low dielectric constant, high glass transition temperature, thermally stable, photopatternable polymers for use as interlayer dielectric layers and as passivation layers which protect microelectronic circuitry. Poly(imides) are widely used to satisfy these needs; these materials, however, have disadvantageous characteristics such as relatively high water sorption and hydrolytic instability. There is thus a need for high performance polymers which can be effectively photopatterned and developed at high resolution.
Polyarylene ethers are known polymers for use as high performance engineering thermoplastics. They exhibit outstanding physical properties and high chemical resistance. The use of these materials as photoresists when substituted with photoactive substituents is also known. These materials are suitable for use in applications such as thermal ink jet printheads, other microelectronics applications, printed circuit boards, lithographic printing processes, interlayer dielectrics, and the like.
Polyarylene ethers are disclosed in U.S. Pat. Nos. 6,087,414, 5,739,254, 5,753,783, 5,761,809, 5,958,995, 6,184,263, 5,945,253, 6,365,323, 5,863,963, 6,090,453, 6,007,877, 6,273,543, 5,814,426, 5,882,814, 5,874,192, 6,273,985, 6,260,956, 6,117,967, 6,177,238, 6,174,636, 6,187,512, 6,020,119, 6,139,920, 6,260,949, 5,773,553, 5,869,595, 5,939,206, 6,485,130, 7,252,927, 7,067,608, and 6,897,267, the disclosures of each of which are totally incorporated herein by reference.
Hyperbranched polymers and processes for the preparation thereof are known. Known syntheses, however, frequently entail the use of custom-synthesized monomers, which can take, for example, two to five steps to prepare prior to synthesis of the hyperbranched polymer. Accordingly, processes which enable the preparation of branched polyarylene ether polymers by direct polymerization of a mixture of monomers, particularly when at least some of the suitable monomers are commercially available, are desirable. Hyperbranched polymers can have several advantages over linear polymers of the same class. For example, branched polymers (hyperbranches and dendrimers) can exhibit a lower solution and melt viscosities compared to their linear analogs owing to their lower hydrodynamic volume for the same molecular weight. In addition, hyperbranched polymers are often more soluble than their linear analogs, which is thought to be attributable to a decrease in the ability of the polymeric material to intertwine at a molecular level. Further, hyperbranched polymers can be thought to be a mid-point between linear polymers and crosslinked polymers, since severing of or more of the branches will not result in a large loss of molecular weight.
Accordingly, while known compositions and processes are suitable for their intended purposes, a need remains for branched polyarylene ether polymers. In addition, a need remains for methods for preparing branched polyarylene ether polymers. Further, a need remains for methods for preparing branched polyarylene ether polymers wherein the synthesis can be carried out by direct polymerization of a mixture of monomers. Additionally, a need remains for methods for preparing branched polyarylene ether polymers wherein at least some of the monomers are commercially available. There is also a need for methods for preparing branched polyarylene ether polymers that enables control of the degree of branching within the polymer and the introduction of branching in a well-defined manner. In addition, there is a need for methods for preparing branched polyarylene ether polymers that can be carried out at desirably low cost levels. Further, there is a need for methods for preparing branched polyarylene ether polymers wherein variations in the ratio of monomers can result in control over the degree of branching and the length of the linear units. Additionally, there is a need for improved photosensitive imaging members. A need also remains for improved binders for photosensitive imaging members. In addition, there is a need for polymeric binders suitable for use in photogenerating layers in imaging members. Further, a need remains for polymeric binders suitable for use in charge transport layers in imaging members. Additionally, a need remains for polymeric binders suitable for use in photosensitive imaging members that can, in some embodiments, impart improved wear resistance to the members, particularly under bias charging roll charging conditions. There is also a need for polymeric binders suitable for use in photosensitive imaging members that can solubilize charge transport materials and other small molecule dopants used to tailor the physical and/or mechanical properties of the imaging members.